In a cylinder head of an engine, a combustion chamber and intake/exhaust ports communicating with the combustion chamber are provided. Then, a valve seat, on which a back face of a valve abuts, is provided in a rim of an opening end of the intake/exhaust port on the combustion chamber side. As the valve seat and the valve abut on each other, airtightness of the combustion chamber is maintained.
Heat resistance and abrasion resistance are required for a valve seat on which a valve abuts repeatedly under a high temperature environment. Therefore, a valve seat is obtained by forming an annular countersunk groove by machining in a rim of an opening end of an intake/exhaust port of a cylinder head blank, and by forming a cladding layer, which is made from a copper based alloy or the like, in the countersunk groove.
As a cladding method for such a valve seat, a laser cladding method is known, in which a cladding layer is formed by supplying metal powder in the countersunk groove and irradiating the metal powder with a laser beam at the same time. For example, Patent Document 1 discloses a cladding method for a valve seat, in which a laser cladding method is used.
Patent Document 1: Japanese Patent Application Publication 04-123885 A (JP 04-123885 A)